The present invention relates to closure elements for containers and, in particular, a tamperproof closure element which is used to seal the necks of bottles and similar containers and assure the user that the contents have not been tampered with prior to first use.
It is known to provide such closure elements integrally molded from synthetic material in which a tear strip is attached to the body of the element by one or two annular zones of reduced strength so as to be easily torn off. This tear strip is used to retain the capsule element on the neck of the container and it is necessary to remove it before having access to the contents of the container.
The manner of providing these zones of reduced strength poses greater problems than might be expected. It is necessary that the tear strip be removed by the user without requiring excessive strength but, at the same time, it must have sufficient resistance to avoid accidental displacement during handling and transport. The requirement that the tear strip be easily removed also conflicts with two other requirements namely, that the reduced strength of the annular zone should not overly diminish the necessary axial rigidity of the closure element nor should it hinder the use of conventional automatic machines for insertion of the closure element. Further, it is important that when forming the closure element by injection molding, the zone of reduced strength should not require restricted flow passages which would cause the molding process to be extremely slow.
These differing requirements have led to different forms of closure element in the prior art. The areas of reduced strength have been produced by grooves or lines of spaced perforations, but neither of these arrangements has been totally satisfactory in practise.